MOSFETs (metal-oxide-semiconductor field-effect transistors) are commonly used in electronic circuits, such as communication systems and power supplies. Power MOSFETs are particularly useful when used as electric switches to enable and disable the conduction of relatively large currents. In some cases, the power MOSFET switch is made bi-directional, i.e., capable of conducting currents equally well in both directions (drain-source and source-drain) within the device. The power MOSFET bi-directional switch (BDS) is typically contained within a monolithic device for ease of integration and system design. Power MOSFET BDS are used in many applications, such as in battery-charging circuitry to permit controlling the charging and discharging of batteries.
The current flow for MOSFETs goes between conduction contacts, e.g., from the source to the drain via the substrate. When creating bi-directional switches, two vertical trench MOSFETS can be used and connected via a common drain. The RDSON (static drain-source on-resistance) should be minimized for power loss and heat dissipation.
A semiconductor device implementing a bi-directional MOSFET power switch is disclosed in International Application No. PCT/US2004/003051, entitled “Bi-Directional Power Switch.” The semiconductor device uses two or more MOSFETs to form the bi-directional power switch. The source terminals of the MOSFETs form the external contacts of the power switch. The drains of the MOSFETs are commonly formed. A control circuit drives the gates of the MOSFETs to enable and disable the power switch. The bi-directional power switch uses a two-metal layer submicron complementary metal oxide semiconductor (CMOS) process. It is desirable to simplify the manufacturing process to achieve lower production costs.
Accordingly, there is a need to provide bi-directional power switches with efficient current flow and without the need for more costly packaging. There is also a need for bi-directional switches with improved on-resistance using low-cost manufacturing processes.